"Cell Population Kinetics as Factor in Tumor Therapy" aims at a quantitative analysis of the effects of therapeutic perturbations on the kinetics of tumor growth. Our chosen assay procedure, the I125- iododeoxyuridine (IUDR 125) prelabeling technique, is now sufficiently refined to permit detailed observations on the rate of tumor cell proliferation, migration, and death of intraperitoneally growing L1210 cells. Preliminary studies indicate that the I125 assay can also be applied to extraperitoneally growing tumor cells. Ideally, our assay should thus permit continuous evaluation of the success of various radiotherapeutic or chemotherapeutic treatment regimens on the rate of death, migration, and proliferation of tumor cells growing in different body compartments. More specifically, the effects of radiation and antimetabolites on tumor growth parameters, as influenced by changes in nutrition, oxygenation, repair capacity, cell concentration, and other variable factors will be studied throughout tumor growth. Attempts will be made to manipulate these factors in such a way that the treatment damage to the tumor cells is maximized while the damage to the host tissues is kept as low as possible.